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수학동아 - 폴리매스
1부터 n까지의 수를 구하는 공식이 n(n+1)/2인데, 왜 그런지 아시는 분 있나요?
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제가 문제로 냈던 거네용 ㅎㅎㅎㅎ
http://www.polymath.co.kr/mathfun/5777
r=1+2+...+n
r=n+(n-1)+...+1
두식을 더하면 2r=(n+1)xn
따라서 r=n(n+1)/2입니다.
라고 하셨던 분도 계시고
A 가 1 ~ n까지 모두 더한 값이면 그것을 거꾸로 (n ~ 1)배열해도 같다.
배열을 순서대로 더해보면 n + 1이 된다. 결국 n + 1이 n개고 그건 2A니까 2로 나누면
n(n + 1)/2다.
...이라고 생각합니다.
라고 하셨던 분도 계십니다
논란이 있으면 댓을 지우겠습니다
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ㅎㅎ그러네요. 대한수학회 37번 문제에 관련 풀이가 있어서 읽어보다가 원리가 궁금해졌어요.
좋아요0
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